The present invention relates to a fluidization coaters for manufacturing coated particles, for example, coated enzyme granules.
Fluidization coaters are useful in coating a bed of particulate seed material or core material to form a coated particulate product. In operation, fluidization coaters continuously fluidize a bed of particles to be treated by lifting the bed of particles in a fluid flow of sufficient air flow volume and velocity to lift the particles and form fluidized bed. The weight of the bed of particles to be coated is limited by the air flow volume and velocity capacities of the fluidization coater. When too heavy a bed of particles is treated in the coater, the weight of the bed of particles can be too great to be fluidized such that dead spots or dead spaces occur in the bed of particles where no fluidization takes place. As a result, the batch of particles resulting from such a process are not uniformly coated and can contain large agglomerates of particles, and uncoated particles. While it has been desirable to process large beds of particles in view of economic concerns, conventional fluidization coaters have been limited in the size of particulate beds that can be processed.
Increasing the air flow and air flow velocity of the fluid flow through a fluidization coater can result in a better ability to fluidize large particle beds, however, in traditional fluidization coaters, increasing the fluid flow and/or fluid flow velocity can lead to a loss of particles through the coater outlet. Therefore, a balance must be reached whereby a fluid flow volume and velocity are used that achieve fluidization of a particulate bed without using too much flow that would lead to undesirably exhausting particles through the coater outlet. It is desirable to provide a fluidization coater that can fluidize and process extremely large beds of particles without wasting particles though an exhaust outlet.
Other problems have been encountered in trying to coat a bed of particles with a fluidization coater. Singular narrow outlets have caused local velocity inconsistencies in coaters including higher local velocities near the outlet, facilitating product xe2x80x9cfly outxe2x80x9d through the coater outlet. Narrow, one-sided fluid outlets also cause non-laminar fluid flow throughout other areas of the coating apparatus resulting in poor fluidization of the bed. Using lower fluid flows to control these problems has not worked and leads to lower manufacturing capacities, bouncing action in the fluidized bed, and difficulties optimizing production as product is fluidized better in one comer or on one side of the apparatus than in another comer or on another side.
Bent, curved, or elbow-jointed inlets have also caused inconsistencies in local fluid flow velocities through coaters. Non-linear inlets have led to fluid flows that are not evenly distributed across a particle retention screen but instead that are of stronger flow volume and/or velocity on one side of the coater than on another side. Thus a portion of a bed above one area of the particle retention screen is often vigorously fluidized while a portion of the bed above a different area of the same screen is not sufficiently fluidized.
As a result of the above problems, undesirable product losses are realized, heat-transfer is inefficient, drying times are increased, production capacity is decreased, and hotter drying temperatures are needed.
The present invention provides a fluidization coater that can process extremely large particle beds while minimizing particle loss through the exhaust outlet of the coater. The present invention achieves this objective by providing a device having a symmetrical design and features that enable an even and uniform distribution of a fluidization flow homogenously through a bed of particles to efficiently fluidize the bed while not causing particles from the bed to be exhausted through a coater outlet. The design of the present invention includes one or more diverging sections in the coating apparatus that reduce the fluid flow velocity by increasing the diameter along the flow path of the fluidization flow. As the diameter increases in the diverging diameter section or sections, the fluid flow velocity decreases sufficiently to allow fluidized particles to settle by gravity back down into the fluidized bed of particles. Throughout the fluidization coater, a symmetrical, even and homogenous flow of fluid is provided. The apparatus can be used in a method of treating particles that benefits from increased capacity, less product loss, better heat transfer properties, better and more uniform coating properties, better drying capacity, better fluidization, and an overall better use of energy compared to conventional fluidization coaters.
Throughout the fluidization coater, a symmetrical, even and homogenous flow of fluid is provided. The apparatus can be used in a method of treating particles that benefits from increased capacity, less product loss, better heat transfer, better and more uniform coating properties, better drying capacity, better fluidization, and an overall better use of energy compared to conventional fluidization coaters.
According to embodiments of the present invention, an evenly distributed fluid flow is passed through a fluid distribution and particle retention plate, herein referred to as a fluid distribution plate, to evenly fluidize a bed of particles otherwise resting on the plate. The inlet system of the device according to the present invention provides a laminar, non-turbulent flow of fluid to the fluid distribution plate which enables the uniform distribution of fluid through the particle bed.
In accordance with an embodiment of the present invention, a fluidized bed coating apparatus is provided that includes a fluid inlet adapted to be connected to a source of fluidizing fluid. The fluid inlet has an entrance opening having a first diameter, an exit opening having a second diameter that is larger than the first diameter, and an expanding inlet section between the entrance opening and the exit opening that has an average diameter that increases in a direction from the entrance opening to the exit opening. The coating apparatus further includes a fluid distribution plate having a plurality of through-passages to allow the passage of fluid therethrough. The fluid distribution plate has an average diameter substantially equal to the average diameter of the exit opening. The side of the fluid distribution plate opposite the side adjacent the exit opening faces a chamber. The chamber has a chamber inlet and a chamber outlet, wherein the fluid distribution plate is positioned between the exit opening and the chamber inlet. Preferably, the chamber has at least a first diverging section having a diverging average diameter that increases in the direction from the chamber inlet toward the chamber outlet. The first diverging section of diverging average diameter provides a fluid flow velocity downstream of the first diverging section that is substantially slower than the fluid flow velocity of fluid reaching the first diverging section from upstream. The coating apparatus also includes a fluid outlet downstream of the chamber outlet for exhausting fluidizing fluid from the coating apparatus.
In accordance with the preferred embodiments of the present invention, the fluid outlet intersects with the chamber outlet at an exhaust port and the exhaust port has an area that is from about 10% to about 130% of the cross-sectional area of the chamber, preferably from about 50% to about 100%.
According to a preferred embodiment of the present invention, the chamber includes first and section diverging sections, each of which has a first diameter at a lower end or first end and a second diameter at an upper end or second end wherein the second diameter is larger than the first diameter. Preferably, the exhaust port includes openings on opposite sides of the chamber.
The coating apparatus of the present invention is preferably of sufficient size and design to employ a fluid flow of from more than about 30,000 m3/hr to about 100,000 m3/hr, or more, and can handle particle beds weighing in excess of 5000 metric tons, for example, beds weighing in excess of 10,000 metric tons. The design can be used with much smaller particle beds to achieve even and homogenous fluid distribution and coating of the particles.
The present invention also relates to a method of coating particles in a bed of particles through the use of a fluidization coater according to the present invention.